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United States Patent |
5,057,865
|
Rosen
,   et al.
|
October 15, 1991
|
Burnout frame with UV-absorption
Abstract
A burnout frame for printing of a transparent original film (4) to a
collecting film or printing plate (1) and a simultaneous burning out of
non-image-carrying areas by means of a light of short wavelength,
comprising a transparent printing glass (6,7,15), which is larger than the
largest original film considered to be printed and which has a clear,
central part (15) of an optical glass and of a type, which absorbs a part
of the light within the ultraviolet wavelength range, particularly a
bronze glass and designed to send light through the original film (4), and
a diffused part (6-7) of a plastic material, located outside said part,
the printing glass on its underside having one or two arrays of vacuum
grooves (8, 9), designed to hold by suction an original film (4) and
possibly also a masking film (5), and the glass part (15) of the printing
glass being inserted into the plastic part (6-7), located on the outside,
and being joined to it by means of a glue (16), which forms a light
barrier between the glass part (15), and the plastic part (6-7),
particularly an optical pure epoxy glue.
Inventors:
|
Rosen; Lars-.ANG.ke (Sollentuna, SE);
Lundberg; Dan J. (Solna, SE)
|
Assignee:
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Misomex Aktiebolag (Hagersten, SE);
Misomex Aktiebolag (Hagersten, SE)
|
Appl. No.:
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605967 |
Filed:
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October 30, 1990 |
Foreign Application Priority Data
Current U.S. Class: |
355/91; 355/125 |
Intern'l Class: |
G03B 027/20 |
Field of Search: |
355/80,85,91,94,122,125
|
References Cited
U.S. Patent Documents
4171903 | Oct., 1979 | Robb | 355/85.
|
4583850 | Apr., 1986 | Thiers | 355/91.
|
4791459 | Dec., 1988 | Hoffman | 355/91.
|
4835576 | May., 1989 | Komori et al. | 355/80.
|
4902899 | Feb., 1990 | Lin et al. | 355/125.
|
4908658 | Mar., 1990 | Lundahl et al. | 355/91.
|
Primary Examiner: Wintercorn; Richard A.
Claims
We claim:
1. A burnout frame of the type, which is used when producing collecting
films, printing plates etc. by printing with a light of short wavelength,
particularly through a so called positive printing, i.e. such a light
printing, in which the printing is done through a positive master, usually
a transparent original film (4) and down to a positive film or plate (1),
the light of short wavelength providing a "burnout" of non-image-carrying
areas in and often also outside the original film, the burnout frame
comprising a transparent printing glass (6,7), which is larger than the
largest original film considered to be printed and which has a clear,
central part (15), designed to send light through the original film (4),
and a diffused part (14), located outside said part, and the printing
glass on its underside having one or two arrays of vacuum grooves (8,9),
designed to hold by suction an original film (4) and possibly also a
masking film (5), which vacuum grooves via ducts (10-13) in the diffused
part (14) of the glass lead to a source of negative pressure,
characterized:
in that the clear, central part of the printing glass is made of an optical
glass (15), whereas the diffused part (14) can be some plastic material;
the central glass being of a type, which absorbs a part of the printing
light radiation, within the ultraviolet wavelength range.
2. A burnout frame according to claim 1, characterized in that the central
glass (15) and the diffused plastic part (6-7) are joined by means of a
glue of a type, which forms a light barrier between the glass part (15)
and the plastic part (6-7).
3. A burnout frame according to claim 1 characterized in that the glass
part (15) of the printing frame is of a type, which absorbs a part of the
light within the wavelength range 350-450 nm.
4. A burnout frame according to claim 1, characterized in that the glass
part (15) of the printing frame is made of a homogenously colored bronze
glass.
5. A burnout frame according to claim 4, characterized in that the glass
part (15) is of a type, which absorbs 5-10% of the light spectrum within
the visible wavelength range.
6. A burnout frame according to claim 2, characterized in that the glass
part (15) and the plastic part (6-7) are joined by means of an optical,
pure and fade resistant epoxy glue.
7. A burnout frame according to claim 6, characterized in that the epoxy
glue in a dried condition is slightly pinkish.
8. A burnout frame according to claim 2 characterized in that the glass
part (15) of the printing frame absorbs light within the wavelength range
350-450 nanometers.
9. A burnout frame according to claim 2 characterized in that the glass
part (15) of the printing frame is made of a homogenously colored bronze
glass.
10. A burnout frame according to claim 8 characterized in that the glass
part (15) of the printing frame is made of a homogenously colored bronze
glass.
Description
The present invention generally relates to a printing frame of the type
which is used when producing films, photosensitive printing plates etc. by
printing with a shortwave light, and the invention relates more
particularly to such a printing frame, which is called a burnout frame and
which is used to produce films and printing plates etc., particularly
through a so called positive printing, i.e. such a light printing, in
which the printing is done through a positive master, usually a
transparent original film and down to a positive film or plate, the
shortwave light causing a "burnout" of non-image-carrying areas in and
often also outside the original film.
A burnout frame of this type is known through the Swedish patennt no.
8704562-1 with laid out-number 458 482. This known burnout frame has a
transparent printing glass, which is larger than the largest original film
considered to be printed. In order to fasten the original film by suction
and possibly the masking film a few grooves are provided on the underside
of the printing glass, which via ducts in the glass lead to a source of
negative pressure. That part of the printing glass, which corresponds to
the largest image surface on the original film is clear, whereas that part
of the printing glass, which is located outside said largest image
surface, has been diffused in such a way, that it allows an exposure
through the printing glass to a film or a plate outside the image-surface
of the original film and in some cases also through the duct-equipped,
diffused part of the printing glass, without the result, that the vacuum
ducts, which extend through this part of the glass, provide shadows, which
form image-carrying areas in the finished film or plate. The printing
glass preferably is made of a transparent plastic material, e.g. an
acrylate material, e.g. Plexi.
A printing frame of this known type provides in many instances an excellent
result, allowing a printing with an optimal exposure time of the
image-carrying areas during a simultaneous burnout, partly of
nonimage-carrying areas of the printing picture and partly also of at
least some areas, located outside the image surface, through the diffused
areas of the printing frame.
However, one problem with the known device is that the exposure latitude in
many instances can be regarded as markedly small, i.e. that the exposure
must be done with a duration and a light intensity, which only is allowed
to vary within very close limits. Partly the exposure ought to be done
with such an intensity and duration, that the image-carrying areas will be
illuminated in the exactly right way, and partly the light intensity and
the duration must be sufficient to burn out the non-image-carrying areas
and at least some areas located outside the picture through the diffused
areas of the printing glass and to prevent the formation of shadows from
the vacuum ducts in the glass.
In some instances the suitable exposure time for the printing film or the
printing plate may provide a too small amount of light to avoid the
formation of shadows from the vacuum ducts in the glass; in other
instances the suitable exposure time for the printing film or the printing
plate maybe is so long, that a light diffusion may take place into the
often demasked, diffused parts of the printing glass, also corresponding
parts of the printing film or printing plate being "burned out" and
rendering impossible a subsequent printing of an image within this part of
the printing film or plate.
Thus, a too brief printing time results in an inferior burning out of
non-image-carrying areas and a risk of a shadow formation from the vacuum
ducts, and a too extended printing time results in a risk of a light
diffusion into an area of the diffused part of the printing glass, which
is placed outside and sometimes is demasked, and consequently a
destruction of the image-receiving layer in this part of the printing film
or the printing plate.
For practical reasons the printing glass in the known device comprised a
plate, including two interacting plastic plates, e.g. a lower plate of an
acrylic plastic, e.g. Plexiglass, and an upper plate of a polyester
plastic, e.g. Makrolon, and the vacuum ducts were formed in the
intermediate layer between these two plastic plates. We have found, that
the light is led in such a way in the plastic layers, that it from the
clear, central part often creeps into the diffused part and partly burns
out the image-receiving layer in the printing film or the printing plate
in such a device. Also, so called Newton-rings between the plastic layers
may be formed, which injuriously influence the exposure. Also, the plastic
layers are susceptible to scratches and easily become staticly charged and
attract dust and other particles.
In order to solve these problems experimental work has been done to insert
a glass plate into that part of the printing glass, which corresponds to
the largest now used original film, i.e. the central, clear part, and to
fasten by gluing this glass plate to the two plastic plates. This has
solved some of the above-mentioned problems, but also with this device the
drawback exists with a comparatively close exposure latitude and the risk
of a diffusion of light into the plastic material in the diffused part of
the printing glass and an ensuing destruction of the image-carrying layer
in the printing film or the printing plate.
Experimental work has shown that the type of glue which is used to fasten
the interior glass plate against the two plastic plates is crucial and may
injuriously influence the result, particularly such a glue which will be
discolored, e.g. be yellow slowly as is the case with some types of glue.
Such a discolored glue maybe will develop such a low transparency, that
image-carrying lines on the printing film or the printing plate,
corresponding to these glue lines, may arise. Many types of glue also
guide the light and provide a not desirable light diffusion in the
duct-equipped plastic part of the printing glass. We have found that an
advantageous glue is an optical pure epoxy glue, which is transparent but
yet forms a type of light barrier between the glass plate and the plastic
plates. The light transparency in a vertical direction is very
satisfactory, despite the fact that the glue, when it dries , will be
slightly pinkish.
It is desirable to be able to vary the exposure of the original film
towards an under-exposure as well as an over-exposure and simultaneously
increase the exposure in the diffused, exterior part of the printing
glass.
In already known devices it has as a rule been necessary to use a certain
overexposure of the original film in order to guarantee that no shadow
formations from the vacuum ducts arise.
We have now found that a particularly satisfactory result can be obtained,
if the glass plate is made of a type of glass, which absorbs a certain
amount of the ultraviolet light. One example of such an efficient glass is
a so called bronze glass, which is a homogenous, slightly
bronze-brown-colored glass, but many other types of glasses can profitably
be used. The color of the glass has no particular importance, since it is
the ultraviolet radiation, which provides the burnout of the
non-image-carrying areas. Since the glass absorbs a part of the
UV-radiation, the exposure can be increased across all the printing glass
without a risk of an overexposure of the image-carrying areas in the
printing film or the printing plate, and simultaneously such a strong
light radiation in the diffused areas, located outside the glass plate, is
obtained, that it has been possible to eliminate the risk of a
shadow-formation from the vacuum ducts completely. In this way partly an
improved burnout of non-image-carrying areas in the printing film or the
printing plate is attained and partly also a sharply increased exposure
latitude, which makes it possible, in an advantageous way, to adjust the
exposure of the original film to various requirements. For some purposes a
certain underexposure perhaps is desirable, for other purposes a certain
overexposure.
The UV-light-suppressing glass preferably absorbs light within the
wavelength range 350-450 nm.
The accompanying drawing shows schematicly a cross-section of a printing
frame according to the invention.
The printing frame shown in the drawing is designed for printing according
to the so called positive method, in which light rays expose or burn out
those areas, which are nonimage-carrying during the printing, from a film
or a printing plate 1, which in a known way is placed on a printing table
2, and against which all the printing frame 3 with the original film 4,
which is sucked into contact with the underside of the printing frame, and
a possibly used masking film 5 can be lowered to a precise contact. The
burned out areas of the printing plate are made non-color-carrying, when
the exposed printing plate is developed.
The printing frame comprises a base plate 6, made of a transparent
material, e.g. an acrylate material, e.g. Plexiglass, which suitably is of
a type, which lacks UV-light-protection, and a covering plate 7, which is
placed on top of this base plate 6 and is fastened to it with an intimate
contact, e.g. by means of a transparent glue, a transparent double-faced
adhesive tape or in another way, which does not interfere with the light
transmission through the composite plate 6-7. The covering plate 7 on top
of plate 6 can be made of some clear, transparent material, e.g. a
polyester material, e.g. Makrolon. Base plate 6 is on its underside
provided with at least two different arrays of vacuum grooves, namely an
exterior groove 8 for holding by sucking an original film 4 and an
interior groove 9 for holding by suction a masking film 5. The two arrays
of vacuum grooves 8 and 9 are via ducts 10 and 11 connected to a source of
negative pressure (not shown).
Vacuum grooves 8 for original film 4 are placed outside the limiting
surface of masking film 5. For practical reasons grooves 8 and 9 are
placed comparatively close to each other. Ducts 10 and 11 are suitably
obtained by cutting grooves in the top face of base plate 6, which grooves
are connected to vertical through holes 12 and 13, which are connected to
lower placed vacuum grooves 8 and 9. The cut grooves on the top face of
base plate 6 are sealed by means of covering plate 7, placed on top of
plate 6. The top face of covering plate 7 is made light diffusing, e.g.
dulled or obscured (blasted) on a surface 14 outside the clear glass
surface above the original film. The object of the dulling of surface 14
is to provide a diffused through beam of light in order to decrease or
eliminate the risk of an emergence of shadows and nonburned-out lines
caused thereby on the collecting film or printing plate 1, due to
refraction phenomena from vacuum grooves 8 and 9 and connection ducts 10
and 11.
As has been mentioned in connection with the discussion of the already
known burnout frame, light, which is directed against the clear glass
surface inside diffused surface 14, may be diffused outwards and into base
plate 6 and covering plate 7 and result in a not desirable illumination
and consequently a burnout of areas in printing plate 1 outside the
image-carrying part of the clear glass surface. This renders a renewed
printing on this second part of the printing plate impossible.
In order to eliminate this problem a square part has been cut out from
composite plastic plate 6-7, and in this cut-out part a plate 15 of glass
has been inserted and fastened by means of a glue line 16 on all sides. We
have found that it is important that a special type of glue be used,
namely a glue, which partly is transparent and does not obstruct a
vertical light transmission down to the printing plate but partly
nevertheless forms a light barrier in the horizontal direction along the
exterior edge of glass plate 15 and consequently obstructs a diffusion of
light into base plate 6 and covering plate 7. Various types of glue have
been tested, not showing satisfactory results. Some types of glue lead the
light out of the glass plate and into the diffusing part of the printing
glass and other types of glue darken, when they dry or later on and
result, when illuminated, in an non-illuminated line on all sides, which
will be image-carrying on printing plate 1. However, one satisfactory glue
has been found, namely an optical pure epoxy glue, which is unfadeable and
which forms a type of light barrier along the edges of glass plate 15, but
which still does not absorb such a large amount of light, that it forms an
image-carrying line on the printing plate, and this is possible despite
the fact that this glue is slightly rose-colored.
By means of the described printing frame original film 4 is exposed
downwards onto the collecting film or printing plate 1, and simultaneously
the non-masked parts of surface 14 of the printing glass outside glass
plate 15 are illuminated. Thus, no extra illumination step is required in
order to burn out those parts outside the original film, which are
supposed to be non-image-carrying.
By means of the described device the flux through the printing frame can be
increased, due to the fact that the risk of light rays outwards from the
edges of the glass plate has been eliminated, and having this stronger
flux it has also been possible to eliminate the risk of shadow-formation
on printing plate 1 from vacuum ducts 10 and 11.
In many instances it is probably desirable to partly obtain a larger
exposure latitude than what has been possible so far or partly increase
the flux against the diffusing surface 14 without simultaneously
increasing the flux through glass plate 15, and in such a case the glass
plate suitably is made of a glass material, which absorbs a certain part
of the ultraviolet light from the lighting of the printing machine,
particularly UV-light within wavelength range 350-450 nm. We have found
that a suitable glass is a homogenous bronze glass, which absorbs a
certain part of the UV-light within the spectrum 350-450 nm and which has
a slight auburn color with an insignificant light reduction, normally a
5-10% light reduction.
Thus, by means of a burnout frame, designed in this way, the flux against
the diffused surface 14 in the printing frame can be increased without any
risk of obtaining any overexposed image-carrying portions in the printing
plate. It will simultaneously be possible to intentionally underexpose the
printing plate without any risk of obtaining shadows from vacuum ducts 10
and 11 on printing plate 1. It is of course also possible to intentionally
overexpose the printing plate, and the device consequently offers a
considerably increased exposure latitude as compared to what has been
possible so far. This in its turn results in a possibility to adjust the
exposure to various types of printing methods and printing machines and to
various desirable printing effects.
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